improvement(corejs): upgrade core-js to version 3.x

Upgrade core-js to version 3.x to gain new featurs and bugfixes. Version 2.x is no longer
maintained.

Author: AtofStryker

Diff for: babel.config.js

@@ -29,8 +29,7 @@ module.exports = api => {
         [
           '@babel/preset-env',
           {
-            // currently, there are dependency resolution issues with older versions of vuepress. Once vuepress is upgraded, core-js can be moved to version 3
-            corejs: 2,
+            corejs: 3,
             useBuiltIns: 'entry'
           }
         ],

Diff for: package.json

@@ -73,7 +73,7 @@
     "babel-jest": "^26.0.1",
     "babel-loader": "^8.1.0",
     "commitizen": "^4.0.3",
-    "core-js": "2",
+    "core-js": "^3.6.5",
     "css-loader": "^4.2.0",
     "cz-conventional-changelog": "^3.0.2",
     "expect": "^26.2.0",

Diff for: yarn.lock

@@ -4669,7 +4669,7 @@ core-js-compat@^3.6.2, core-js-compat@^3.6.5:
     browserslist "^4.8.5"
     semver "7.0.0"
 
-core-js@2, core-js@^2.4.0, core-js@^2.5.0:
+core-js@^2.4.0, core-js@^2.5.0:
   version "2.6.11"
   resolved "https://registry.yarnpkg.com/core-js/-/core-js-2.6.11.tgz#38831469f9922bded8ee21c9dc46985e0399308c"
   integrity sha512-5wjnpaT/3dV+XB4borEsnAYQchn00XSgTAWKDkEqv+K8KevjbzmofK6hfJ9TZIlpj2N0xQpazy7PiRQiWHqzWg==